I don't think their open sourcing is some kind of desperate attempt. They open sourced .NET understanding that developer tools and languages have to be open source nowadays, if they want adoption.
Most devs beside enterprise IT departments use open source languages for web deveopment. NodeJS/Java/PHP/Ruby/Python/Go are very popular and only a tiny fraction (11%) runs on Windows servers with dotNet or Mono. http://news.netcraft.com/archives/2015/11/16/november-2015-w...
I know if you nmap our website which uses iis it returns as something else because of our load balancer.